Conjugated diene rubber (e.g. a styrene-butadiene copolymer) produced by a method of emulsion polymerization has been known as rubber used for car's tires. Under recent circumstances where improvements in low fuel consumption propoerty of cars have been expected, various types of conjugated diene rubber capable of achieving excellent low fuel consumption propoerty have been proposed.
As an example of such rubber, conjugated diolefin (co)polymer rubber has been proposed (Patent Document 1) which (1) is (co)polymer rubber of conjugated diolefin(s) or copolymer rubber of a conjugated diolefin and an aromatic vinyl compound and (2) has primary amino groups and alkoxysilyl groups binding to its (co)polymeric chain, and wherein (3) monomers having bifunctionality or more are copolymerized in its (co)polymeric chain and/or a coupling agent having bifunctionality or more is coupled to at least part of its (co)polymeric chain.
As other example of such rubber, modified diene polymer rubber has been proposed (Patent Document 2) which is produced in a process including a step 1 at which an active polymer with an alkali metal terminal is produced by polymerization of a conjugated diene monomer or polymerization of a conjugated diene monomer with an aromatic vinyl monomer in a hydrocarbon solvent in the presence of an alkali metal catalyst and a step 2 at which modified polymer rubber is produced by reaction between the active polymer and a compound represented by a specific formula.
In addition, as a method of producing a modified polymer capable of obtaining improvements in fracture characteristics, abrasion resistance and low-exothermic properties through increases in interactions with silica and carbon black, there is a proposed method (Patent Document 3) wherein a primary modification reaction is performed by making a polymer having an organometallic active site in its molecule react with a hydrocarbyloxysilane compound at the active site, and then a secondary modification reaction is performed by subjecting the hydrocarbyloxysilane compound to a reaction via condensation reaction between hydrocarbyloxysilyl groups.
Further, as a method of producing a modified conjugated diene polymer for solution of problems which are likely to arise in low-exothermic rubber compositions (such as problems of being low in Mooney viscosity and inferior in shape stability), a method of producing a modified conjugated diene polymer has been proposed (Patent Document 4) which includes a process step (a) wherein a primarily modified polymer is produced by using a conjugated diene polymer having an alkali metal active terminal obtained by anionic polymerization of at least a diene monomer in the presence of an alkali metal initiator in a hydrocarbon solvent and a process step (b) wherein a secondarily modified polymer (modified conjugated diene polymer) is produced through a step (b1) wherein the primarily modified polymer produced is made to react with a condensation accelerator containing metal element(s) and a step (b2) wherein at least one compound chosen from among inorganic acids or metal halides, respectively.